The present invention is related to variable valve train systems for use on internal combustion engines; more particularly, to devices for controllably varying the lift of valves in such engines; and most particularly, to a variable valve train device driven by an input crankshaft and employing a ring and planetary gear arrangement that controllably varies the lift of the intake valves to control engine load.
Internal combustion engine performance has progressed considerably in the past century. Inventions have yielded cleaner exhaust and enhanced durability, fuel efficiency, and power. Systems for varying the lift and timing of intake valves can further refine and enhance the performance of the internal combustion engine by controllably varying the volume of fuel mix supplied to the combustion chambers as a function of engine load and rotational speed. Fuel economy at part load operation can be increased by promoting more thorough combustion, reducing pumping work done by the pistons, which saps energy, deactivating cylinders, and/or by implementing a lean air/fuel ratio scheme. Matching the intake valve closing time more closely to the engine""s need can enhance driveability of a vehicle by improving engine breathing at full engine load. Moreover, if intake and exhaust events can be controlled sufficiently to vary engine load, speed, and fuel dilution over the entire spectrum of required engine operating conditions, a controllable variable valve train can obviate the need for a throttle valve and EGR valve in a gas or diesel internal combustion engine.
A range of variable valve train devices and valve timing mechanisms for enhancing engine performance are known in the automotive art, but commercial use of such devices generally has been impractical because of cost, size, and/or operating limitations which have limited their true value and practicality. For example, variable valve timing (VVT) mechanisms, as disclosed in U.S. Pat. No. 5,937,809 issued Aug. 17, 1999 to Pierik et al. and U.S. Pat. No. 6,019,076 issued Feb. 1, 2000 to Pierik et al., the relevant disclosures of both patents being incorporated herein by reference, employ a segmented single shaft crank rocker (SSCR) for operating individual or multiple engine valves by engaging a linkage with a rotary eccentric, preferably a rotary cam, to drive an oscillatable rocker cam. The disclosed SSCR mechanism has four moving components (two arms, a rocker, and a cam) and thus can be expensive to manufacture and subject to wear and premature failure at a plurality of joints. In addition, in typical prior art VVTs, springs are required to maintain contact between an input cam and a roller follower, which springs tend to increase friction and limit maximum operating speed.
It is a principal object of the present invention to provide total authority over intake valve lift, open valve duration, and phasing of intake and exhaust events relative to the motion of an engine""s pistons.
It is a further object of the invention to improve peak engine torque and fuel economy.
It is a still further object of the invention to controllably vary the engine load directly at the engine cylinder, thereby potentially eliminating the need for prior art throttle body and idle air control devices.
It is a still further object of the invention to reduce the size and number of components of the device in comparison with prior art variable valve train devices.
It is a still further object of the invention to provide a variable valve train device which can be economically mass-produced for commercial use in vehicles powered by internal combustion engines.
Briefly described, a ring gear variable valve train device in accordance with the invention is provided for installation on an internal combustion engine having a rotary input shaft positioned substantially as is a camshaft in a conventional engine. The basic mode of operation is similar to that disclosed in the patents incorporated by reference, wherein a variable valve train apparatus is mounted on an input shaft of an engine, such as a camshaft, and is pivotable about the shaft to alter the timing and lift of a valve opening upon an engine""s cylinder. In the present invention, the input shaft, rather than being a conventional camshaft and having an eccentric cam lobe, is provided with a cylindrical eccentric journal having a center offset from the rotational axis of the shaft such that a connecting rod may be disposed conventionally on the journal for deriving reciprocating motion from the rotary motion of the input shaft. A close-fitting frame is rotationally disposed on the camshaft such that the input shaft and journal are free to rotate within the frame. The frame is pivotably connected to an auxiliary control shaft such that the angular orientation of the frame with respect to the input shaft may be controllably varied to vary the lift and timing of the valve. A rocker arm is pivotably disposed on the frame and is attached to the connecting rod to oscillate an arcuate ring gear portion of the rocker arm in response to rotary motion of the input shaft. The ring gear portion meshes with and drives a planetary-geared output cam rotatably disposed on the input shaft to actuate the stem of an engine intake valve to open and then to close the valve conventionally against a valve spring. Preferably, the teeth of the ring gear and the planetary gear are axially tapered in opposite directions, such that a coil spring disposed in compression on the output shaft is operative axially against a side face of the planetary gear to displace the planetary gear axially until all lash is eliminated between the two gears. In a preferred embodiment for controlling the motion of two parallel valves at a single engine cylinder, the elements of the frame, ring gear portion, and output cam are doubled symmetrically about the input shaft journal, and a dual rocker arm cooperates with both ring gear portions for simultaneous and identical actuation thereof. Rotation of the frame about the input shaft serves to alter the timing of the valve opening with respect to the associated piston, the height of the valve lift, and the duration of opening. Preferably, each cylinder in an internal combustion engine is provided with an individual device in accordance with the present invention. The disclosed invention is thus capable of controlling engine load and peak engine torque directly at the cylinder head without resort to a conventional throttle and exhaust gas recirculation (EGR) valve. The invention is also useful for variably controlling the valves of other apparatus incorporating pintle-type valves, for example, compressors for air and other gases.